An image sensor provides a grid of pixels, such as photosensitive diodes or photodiodes, reset transistors, source follower transistors, pinned layer photodiodes, and/or transfer transistors for recording an intensity or brightness of light. The pixel responds to the light by accumulating a charge. The charge can then be used by other circuits so that a color and brightness can be used for a suitable application, such as a digital camera. Common types of pixel grids include a charge-coupled device (CCD) or complimentary metal oxide semiconductor (CMOS) image sensor (CIS). Backside illuminated image sensors are used for sensing a volume of exposed light projected towards the backside surface of a substrate. The pixels are located on a front side of the substrate, and the substrate is thin enough so that light projected towards the backside of the substrate can reach the pixels. Backside illuminated image sensors provide a high fill factor and reduced destructive interference, as compared to front-side illuminated sensors.
As part of manufacturing the backside illuminated image sensors, the trench isolation structures serve to separate one pixel from a second pixel in the pixel region, and serve to separate one or more components in the peripheral circuit region. The conventional trench isolation structures in a silicon substrate have the same depth in the pixel region and the peripheral circuit region, which may not adequately isolate one pixel area from another. The depth of the conventional trench isolation structure may not be sufficient to keep a photo-generated carrier from a first pixel region to a second pixel region. This can cause leakage current to the sensor devices, and electrical crosstalk and defects such as dark current, white pixel and blooming to degrade the performance of the backside illuminated image sensors.